One type of dental implant has a post stem integrally attached through a short neck to a head for receiving a dental appliance, such as an artificial tooth. The post is inserted into a relatively deep socket or osteotomy formed in the alveolar bone so that the neck extends through the gingiva while the head protrudes above the surface of the gums. Typically, post stems have uneven outer surfaces for fixation within the alveolar bone through tissue ingrowth. An example of a dental implant having a post stem with an undulating surface is found in U.S. Pat. No. 4,195,409.
As a means of providing immediate immobilization of a dental implant within the alveolar bone, it is common practice to slightly undersize the socket and to force the stem thereinto. Unfortunately, the success rate of post stem dental implants has been less than would be desirable. The porous alveolar bone is particularly subject to deterioration, and it is believed that bone damage incurred by forcing an oversized stem into a narrow socket may accelerate bone deterioration. Hence, while forcing an oversize stem into a narrow socket may provide immediate immobilization, the fixation through tissue ingrowth, necessary for long-term stability, may not occur. Subsequent bone deterioration may actually result in loosening of the implant, and if this occurs, the implant may have to be removed.
Another cause of failure of post stem implants is the imprecision of the drilling operations which form the socket. Frequently, post stems are tapered for insertion into tapered sockets. Such sockets are commonly formed by a succession of drillings with several drill bits of different diameters. This process is slow and may result in burning of the bone tissue and other trauma. Frequently, due to imprecise drilling, the result of the successive drillings is not the desired undersized socket, but an oversized socket in which the implant fits loosely. An implant which is not immediately immobilized usually shifts when subjected to the stresses of mastication causing failure of the implant.
The need continues for dental prostheses which may be implanted with minimal disruption to the alveolar bone into which they are inserted and which have no mobility in the socket immediately after implantation.